1. Field of the Invention
The present invention relates to the production of liquid fuels, particularly diesel and naphtha fuels, from vegetable and/or animal oils.
2. Description of the Related Art
Most combustible liquid fuels used for on road, off road, stationary engines, and combustion turbines and boilers in the world today are derived from crude oil. However, there are several limitations to using crude oil as a fuel source. For example, crude oil is in limited supply, includes a high content of aromatics, and contains sulfur and nitrogen-containing compounds that can adversely affect the environment. There is a great desire and need in the industry to provide combustible liquid fuels that are more environmentally friendly, display good engine performance, and which are available from alternative sources that are abundantly renewable.
Vegetable and animal oils are an abundant and renewable source. The use of vegetable oil in diesel engines requires significant engine modification, including changing of piping and injector construction materials, otherwise engine running times are decreased, maintenance costs are increased due to higher wear, and the danger of engine failure is increased. The current conversion of vegetable and animal oils to combustible liquid fuels typically involves transesterification of the oils, which are triglycerides of C14 to C22 straight-chain carboxylic acids, with a lower alcohol such as methanol or ethanol, to form a mixture of methyl or ethyl esters called “biodiesel”. This process is relatively complex, typical of the chemical industry rather than the petrochemical industry. Furthermore, the composition of biodiesel, which is completely different from that of diesel produced from crude oil, may have adverse effects on engine performance. Biodiesel exhibits poor low temperature performance characteristics and increased nitrogen oxide (NOx) emissions compared to conventional fuels derived from crude oil.
In the search for alternative and renewable sources, there is increasing interest in producing liquid fuels from biological raw materials for use as fuel by themselves or in mixture with the petroleum-derived fuels in use today. The patent literature describes methods for producing hydrocarbon mixtures from biological sources, including vegetable oils.
United Kingdom Patent Specification 1 524 781 discloses converting ester-containing vegetable oils into one or more hydrocarbons by pyrolysis at 300 to 700° C. in the presence of a catalyst which comprises silica-alumina in admixture with an oxide of a transition metal of Groups IIA, IIIA, IVA, VA, VIA, VIIA or VIII of the periodic table, preferably in a fluidized bed, moving bed or fixed bed tubular reactor at atmospheric pressure.
U.S. Pat. No. 5,705,722 discloses a process for producing additives for diesel fuels having high cetane numbers and serving as fuel ignition improvers. In the process, biomass feedstock selected from (a) tall oil containing less than 0.5 wt % ash, less than 25 wt % unsaponifiables, up to 50 wt % diterpenic acids and 30 to 60 wt % unsaturated fatty acids, (b) wood oils from the pulping of hardwood species, (c) animal fats and (d) blends of said tall oil with plant or vegetable oil containing substantial amounts of unsaturated fatty acids or animal fats, is subjected to hydroprocessing by contacting the feedstock with gaseous hydrogen under hydroprocessing conditions in the presence of a hydroprocessing catalyst to obtain a product mixture. This product mixture is then separated and fractionated to obtain a hydrocarbon product boiling in the diesel fuel boiling range, this product being the high cetane number additive.
U.S. Patent Publication No. 2004/0055209 discloses a fuel composition for diesel engines comprising 0.1-99% by weight of a component or a mixture of components produced from biological raw material originating from plants and/or animals and/or fish and 0-20% of components containing oxygen. Both components are mixed with diesel components based on crude oil and/or fractions from Fischer-Tropsch process.
U.S. Patent Publication No. 2004/0230085 discloses a process for producing a hydrocarbon component of biological origin comprising at least two steps, the first one of which is a hydrodeoxygenation step and the second one is an isomerization step operated using the counter-current flow principle. A biological raw material containing fatty acids and/or fatty acid esters serves as the feed stock.
Fuel properties important for potential diesel applications include: (i) lubricity; (ii) cetane number; (iii) density; (iv) viscosity; (v) lower heating value; (vi) sulfur; (vii) flash point; (viii) cloud point; (ix) Distillation Curve; (x) carbon residue; (xi) ash; and (xii) Iodine Value. Lubricity affects the wear of pumps and injection systems. Lubricity can be defined as the property of a lubricant that causes a difference in friction under conditions of boundary lubrication when all the known factor except the lubricant itself are the same; thus, the lower the friction, the higher the lubricity. Cetane number rates the ignition quality of diesel fuels. Density, normally expressed as specific gravity, is defined as the ratio of the mass of a volume of the fuel to the mass of the same volume of water. Viscosity measures the fluid resistance to flow. Lower heating value is a measure of available energy in the fuel. Flash point is the lowest temperature at which a combustible mixture can be formed above the liquid fuel. Cloud point measures the first appearance of wax. Distillation Curve is characterized by the initial temperature at which the first drop of liquid leaves the condenser and subsequent temperatures at each 10 vol % of the liquid. Carbon residue correlates with the amount of carbonaceous deposits in a combustion chamber. Ash refers to extraneous solids that reside after combustion. Iodine Value measures the number of double bonds.
A comparison of properties of biodiesel and EN standard EN590:2005 diesel can be found in Table 1.
TABLE 1EN590Fuel PropertyBiodieselDieselDensity @ 15° C., kg/m3≈885≈835Viscosity @ 40° C., mm2/s≈4.5≈3.5Cetane Number≈51≈5390 vol % Distillation, ° C.≈355≈350Cloud Point, ° C.≈−5≈−5Lower Heating Value, MJ/kg≈38≈43Lower Heating Value, MJ/liters≈34≈36Polyaromatics, wt %0≈4Oxygen, wt %≈110Sulfur, mg/kg<10<10
The American Society for Testing and Materials (ASTM) standards for commercial diesel (ASTM D975) and biodiesel (ASTM D6751) can be found in Table 2.
TABLE 2DieselBiodieselFuel PropertyASTM D975ASTM D6751Lower Heating Value, BTU/gal129,050118,170Kinematic Viscosity @ 40° C., cSt1.3-4.14.0-6.0Specific Gravity @ 60° C., g/cm30.850.88Carbon, wt %8777Hydrogen, wt %1312Oxygen, by dif. wt %011Sulfur, ppm5000Boiling Point, ° C.180 to 340315 to 350Flash Point, ° C.60 to 80100 to 170Cloud Point, ° C.~15 to 5 ~3 to 12Pour Point, ° C.~35 to ~15~15 to 10 Cetane Number40-5548-65Lubricity (HFRR), μm300-600<300
There remains a need for alternative processes for conversion of vegetable and animal oils to fuels and diesel fuel compositions derived from vegetable and animal oils having better and more acceptable properties.